Abstract: The low energy proton irradiation will cause a large loss of non-ionizing energy on the solar cells and lead to a decrease of minority carrier lifetime, thus destroying the electrical properties of the GaInP/GaAs/Ge. In particular, the degradation of the GaAs sub-cell is the most serious. In this paper, a single-junction GaAs cell with the same structure as the GaAs sub-cell in the triple-junction solar cells was prepared. The properties of the single-junction GaAs cell irradiated by 150 keV proton were tested. The results show that after 150 keV proton irradiation, the degradation of the base region is the most serious. Based on the photoluminescence results, the non-radiative minority carrier lifetimes are 2.22, 0.67 and 0.13 ns at the irradiation fluence of 3×10¹⁰, 1×10¹¹ and 5×10¹¹ cm^-2 respectively. Based on the above results, the physical model of GaAs was established by using multi-physical field software COMSOL, and the degradation of GaAs sub-cell was simulated. The experimental results were compared with the simulation results, and the maximum relative deviation between them is 7%. The simulation results show that the radiation damage of GaAs solar cells on the Chinese Space Station mainly is induced by earth’s trapped proton and the degradation of maximum power after 5 years is about 7.6% in solar maximum and about 13.7% in solar minimum.